Recently, there have been known compact analog timepieces, such as watches, provided with only one motor and a hand moving mechanism for simultaneously moving a seconds hand, a minute hand, and an hour hand according to the driving timing of the motor and those provided with a plurality of motors so that a seconds hand and minute and hour hands, or a seconds hand, a minute hand, and an hour hand are separately driven according to the driving timings of the motors.
Analog timepieces which drive three hands by one motor are inferior in terms of flexibility in driving control to analog timepieces which drive hands by a plurality of motors because they have to drive all the three hands by one motor.
When a seconds-hand moving mechanism and an hour-and-minute-hand moving mechanism are independently driven by two motors, hand-moving timings match the driving timings of the motors. Therefore, if the seconds-hand and the hour-and-minute-hand moving timings are the same, a seconds motor and an hour-and-minute motor are driven at the same time. A current load for driving the motors occur at that time and a problem arises in that a power-supply voltage is reduced.
To prevent the power-supply voltage from decreasing, it can be considered that different intervals are used for the driving timings of the seconds motor and the hour-and-minute motor. In this case, a problem occurs in that a difference between the hand-moving timings for the seconds hand and the hour and minute hands becomes conspicuous to the user.
The above-discussed problems will be specifically described below.
FIG. 11 shows the structure of a general driving control system in a time measuring apparatus, which is a prerequisite for the following description.
As shown in FIG. 11, a driving control circuit 24 generates a driving-pulse control signal, and sends the generated driving-pulse control signal to an hour-and-minute driving circuit 30m and to a seconds driving circuit 30s. The hour-and-minute driving circuit 30m and the seconds driving circuit 30s send an hour-and-minute driving-pulse signal to an hour-and-minute motor 10m and a seconds driving-pulse signal to a seconds motor 10s, respectively, according to the driving-pulse control signal sent from the driving control circuit 24.
The hour-and-minute motor 10m and the seconds motor 10s drive the hour-and-minute motor 10m and the seconds motor 10s to move hands by the hour-and-minute driving-pulse signal and the seconds driving-pulse signal sent from the hour-and-minute driving circuit 30m and the seconds driving circuit 30s, respectively.
The driving control circuit 24 is also provided with a function for detecting the rotations of the hour-and-minute motor 10m and the seconds motor 10s according to induced voltages generated at driving coils not shown by the rotations of the motors, and a function for detecting magnetic fields around the hour-and-minute motor 10m and the seconds motor 10s according to induced voltages generated at the driving coils not shown by the surrounding magnetic fields.
The driving control circuit 24 determines with the use of the above-described rotation detection function whether the hour-and-minute motor 10m and the seconds motor 10s correctly rotate by the hour-and-minute driving-pulse signal, and also determines with the use of the magnetic-field detection function whether an external magnetic field which affects the normal functioning of the rotation detection function exists around the hour-and-minute motor 10m and the seconds motor 10s.
A detailed description will be given by referring to FIG. 10.
When the seconds hand and the hour and minute hands are driven by the motors in that order, for example, the driving control circuit 24 outputs the seconds driving-pulse signal K1s6 to the seconds driving circuit 30s to drive the seconds hand as shown by the pulse timing Os6 in FIG. 10.
After outputting the seconds driving-pulse signal K1s6, the driving control circuit 24 outputs a seconds rotation-detection-pulse signal SP2s6 used for checking whether the seconds hand has correctly rotated.
If a correct rotation is not detected by the use of the seconds rotation-detection-pulse signal SP2s6, the driving control circuit 24 outputs a seconds auxiliary pulse signal P2s6 used for positively driving the seconds hand, which is larger in effective electric power than the seconds driving-pulse signal K1s6, to drive the seconds motor 10s.
As shown by the pulse timing Om6 in FIG. 10, the driving control circuit 24 outputs an hour-and-minute driving-pulse signal K1m6 to the hour-and-minute driving circuit 30m to drive the hour and minute hands.
The period of time T61 shown in FIG. 10 indicates the maximum period between the seconds-hand moving timing and the hour-and-minute-hand moving timing. If the period of time T61 is long, the difference between the seconds-hand moving timing and the hour-and-minute-hand moving timing becomes conspicuous to the user.
The period of time T62 shown in FIG. 10 indicates the minimum period between the seconds-hand moving timing and the hour-and-minute-hand moving timing. If the period of time T62 is short and current loads caused by the driving of the hour-and-minute motor 10m and the seconds motor 10s, which drive the hour and minute hands and the seconds hand, overlap, the power-supply voltage is reduced and in some cases, incorrect hand movement may be performed.
When the seconds hand and the hour and minute hands are driven with the period of time T61 being set such that the difference between the seconds-hand moving timing and the hour-and-minute-hand moving timing does not become conspicuous to the user, it is understood from the above description that the period T62 becomes too short and a problem arises in that the hour-and-minute driving-pulse signal K1m6 is output before the power-supply voltage has recovered from a reduced voltage caused by the output of the seconds auxiliary pulse signal P2s6 after the seconds auxiliary pulse signal P2s6 has been output.